/Engine/Source/Runtime/UMG/Public/Components/Widget.h
We recommend not to use this data unless there's no other way to solve your problem. Normally in Slate we try and handle these issues by making a dependent widget part of the hierarchy, as to avoid frame behind or what are referred to as hysteresis problems, both caused by depending on geometry from the previous frame being used to advise how to layout a dependent object the current frame.
const [FGeometry](API\Runtime\SlateCore\Layout\FGeometry) & GetCachedGeometry() const